12. Beyond the Standard Model Particle and Nuclear Physics

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Dr. Tina Potter

Dr. Tina Potter 12. Beyond the Standard Model 1 In this section...

Summary of the Standard Model Problems with the Standard Model Neutrino oscillations Supersymmetry

Dr. Tina Potter 12. Beyond the Standard Model 2 The Standard Model (2012)

1 Matter: point-like spin 2 Dirac fermions

Fermion Charge [e] Mass Electron e− −1 0.511 MeV Electron neutrino νe 0 ∼ 0 gen.

st Down quark d −1/3 4.8 MeV 1 Up quark u +2/3 2.3 MeV Muon µ− −1 106 MeV Muon neutrino ν 0 ∼ 0 gen. µ

nd Strange quark s −1/3 95 MeV 2 Charm quark c +2/3 1.3 GeV Tau τ − −1 1.78 GeV Tau neutrino ν 0 ∼ 0

gen. τ

rd Bottom quark b −1/3 4.7 GeV 3 + antiparticles Top quark t +2/3 173 GeV

Dr. Tina Potter 12. Beyond the Standard Model 3 The Standard Model (2012) Forces: mediated by spin 1 bosons Force Particle Mass Electromagnetic Photon γ 0 Strong 8 gluons g 0 Weak (CC) W ± 80.4 GeV Weak (NC) Z 91.2 GeV The Standard Model also predicts the existence of a spin-0 Higgs boson which gives all particles their masses via its interactions. Evidence from LHC confirms this, with mH ∼ 125 GeV. The Standard Model successfully describes all existing particle physics data, with the exception of one ⇒ Neutrino Oscillations ⇒ Neutrinos have mass In the SM, neutrinos are treated as massless; right-handed states do not exist ⇒ indication of physics Beyond the Standard Model Dr. Tina Potter 12. Beyond the Standard Model 4 Problems with the Standard Model The Standard Model successfully describes all existing particle physics data (though question marks over the neutrino sector). But: many (too many?) input parameters: Quark and lepton masses Quark charge 2 Couplings αEM, sin θW , αs Quark (+ neutrino) generation mixing – VCKM and: many unanswered questions: Why so many free parameters? Why only three generations of quarks and leptons? Where does mass come from? (Higgs boson probably OK) Why is the neutrino mass so small and the top quark mass so large? Why are the charges of the p and e identical? What is responsible for the observed matter-antimatter asymmetry? How can we include gravity? etc Dr. Tina Potter 12. Beyond the Standard Model 5 Beyond the Standard Model – further unification?? Grand Unification Theories (GUTs) aim to unite the strong interaction with the electroweak interaction. Underpins many ideas about physics beyond the Standard Model. The strength of the interactions depends on energy:

Suggests uniﬁcation of all forces at ∼ 1015 GeV? Strength of Gravity only signiﬁcant at the Planck Mass ∼ 1019 GeV Dr. Tina Potter 12. Beyond the Standard Model 6 Neutrino Oscillations In 1998 the Super-Kamiokande experiment announced convincing evidence for neutrino oscillations implying that neutrinos have mass.

π → µνµ ,→ eνµν¯e

Expect N(ν ) µ ∼ 2 N(νe)

Super-Kamiokande results indicate a deﬁcit of νµ from the upwards direction. Upward neutrinos created further away from the detector.

Interpreted as νµ → ντ oscillations Implies neutrino mixing and neutrinos have mass Dr. Tina Potter 12. Beyond the Standard Model 7 Detecting Neutrinos Neutrinos are detected by observing the lepton produced in charged current − + interactions with nuclei. e.g. νe + N → e + X ν¯µ + N → µ + X Size Matters: −42 2 Neutrino cross-sections on nucleons are tiny; ∼ 10 (Eν/ GeV)m Neutrino mean free path in water ∼ light-years. Require very large mass, cheap and simple detectors. Water Cerenkovˇ detection Cerenkovˇ radiation Light is emitted when a charged particle traverses a dielectric medium A coherent wavefront forms when the velocity of a charged particle exceeds c/n (n = refractive index) Cerenkovˇ radiation is emitted in a cone i.e. at ﬁxed angle with respect to the particle.

c 1 cos θ = = C nv nβ

Dr. Tina Potter 12. Beyond the Standard Model 8 Super-Kamiokande

Super-Kamiokande is a Water Cerenkovˇ detector sited in Kamioka, Japan

50, 000 tons of water Surrounded by 11, 146 × 50 cm diameter, photo-multiplier tubes

Dr. Tina Potter 12. Beyond the Standard Model 9 Super-Kamiokande Examples of events − − νµ + N → µ + X νe + N → e + X

Dr. Tina Potter 12. Beyond the Standard Model 10 Super-Kamiokande ν deﬁcit

No oscillations With oscillations Data Expect Isotropic (ﬂat) distributions in cos θ e-like N(νµ) ∼ 2N(νe)

Observe

Deﬁcit of νµ from below Whereas νe look as expected μ-like Interpretation

νµ → ντ oscillations ⇒ neutrinos have mass

Dr. Tina Potter 12. Beyond the Standard Model 11 Neutrino Mixing The quark states which take part in the weak interaction (d 0, s0) are related to the flavour (mass) states (d, s) 0 Weak Eigenstates d cos θC sin θC d Mass Eigenstates 0 = ◦ s − sin θC cos θC s Cabibbo angle θC ∼ 13 Suppose the same thing happens for neutrinos. Consider only the first two generations for simplicity. ν cos θ sin θ ν Mass Eigenstates Weak Eigenstates e = 1 = flavour eigenstates νµ − sin θ cos θ ν2 Mixing angle θ + + e.g. in π decay produce µ and νµ i.e. the neutrino state that couples to the weak interaction.

The νµ corresponds to a linear combination or expressing the mass eigenstates of the states with deﬁnite mass, ν1 and ν2 in terms of the weak eigenstates νe = +ν1 cos θ + ν2 sin θ ν1 = +νe cos θ − νµ sin θ νµ = −ν1 sin θ + ν2 cos θ ν2 = +νe sin θ + νµ cos θ Dr. Tina Potter 12. Beyond the Standard Model 12 Neutrino Mixing

Dr. Tina Potter 12. Beyond the Standard Model 13 Neutrino Mixing

Suppose a muon neutrino with momentum p~ is produced in a weak decay, e.g. + + π → µ νµ At t = 0, the wavefunction ψ(p~, t = 0) = νµ(p~) = ν2(p~) cos θ − ν1(p~) sin θ

The time evolution of ν1 and ν2 will be diﬀerent if they have diﬀerent masses

−iE1t −iE2t ν1(p~, t) = ν1(p~)e ; ν2(p~, t) = ν2(p~)e

After time t, state will in general be a mixture of νe and νµ

−iE2t −iE1t ψ(p~, t) = ν2(p~)e cos θ − ν1(p~)e sin θ

−iE2t −iE1t = [νe(p~) sin θ + νµ(p~) cos θ] e cos θ − [νe(p~) cos θ − νµ(p~) sin θ] e sin θ

2 −iE2t 2 −iE1t −iE2t −iE1t = νµ(p~) cos θe + sin θe + νe(p~) sin θ cos θ e − e

= cµνµ(p~) + ceνe(p~)

Dr. Tina Potter 12. Beyond the Standard Model 13 Neutrino Mixing

Probability of oscillating into νe 2 2 −iE2t −iE1t P(νe) = |ce| = sin θ cos θ e − e 1 = sin2 2θ e−iE2t − e−iE1t eiE2t − eiE1t 4 1 = sin2 2θ 2 − ei(E2−E1)t − e−i(E2−E1)t 4 (E − E )t = sin2 2θ sin2 2 1 2 s p m2 m2 But E = p~ 2 + m2 = p~ 1 + ∼ p~ + for m E p~ 2 2p~ 1 + x ∼ (1 + x/2)2 when x is small, can ignore x 2 term m2 − m2 m2 − m2 ⇒ E (p~) − E (p~) ∼ 2 1 ∼ 2 1 2 1 2p~ 2E (m2 − m2)t ⇒ P(ν → ν ) = sin2 2θ sin2 2 1 µ e 4E Dr. Tina Potter 12. Beyond the Standard Model 14 Neutrino Mixing

2 2 2 For ν → ν 2 2 (m3 − m2)t 2 2 1.27∆m L µ τ P(νµ → ντ ) = sin 2θ sin = sin 2θ sin 4E Eν where L is the distance travelled in km, 2 2 2 2 ∆m = m3 − m2 is the mass diﬀerence in ( eV) and Eν is the neutrino energy in GeV. Interpretation of Super-Kamiokande Results

For E(νµ) = 1 GeV (typical of atmospheric neutrinos)

Results are consistent with νµ → ντ oscillations: 2 2 −3 2 2 |m3 − m2| ∼ 2.5 × 10 eV ; sin 2θ ∼ 1 Dr. Tina Potter 12. Beyond the Standard Model 15 Neutrino Mixing – Comments

Neutrinos almost certainly have mass Neutrino oscillation only sensitive to mass diﬀerences More evidence for neutrino oscillations Solar neutrinos (SNO experiment) Reactor neutrinos (KamLand) 2 2 −5 2 suggest |m2 − m1| ∼ 8 × 10 eV . More recent experiments use neutrino beams from accelerators or reactors; observe energy spectrum of neutrinos at a distant detector.

At ﬁxed L, observation of the values of Eν at which minima/maxima are seen determines∆ m2, while depth of minima determine sin2 2θ. Note all these experiments only tell us about mass diﬀerences. Best constraint on absolute mass comes from the end point in Tritium β-decay, m(νe) < 2 eV.

Dr. Tina Potter 12. Beyond the Standard Model 16 Three-ﬂavour oscillations     This whole framework can be generalised... νe ν1  νµ  = UPNMS  ν2  ντ ν3  1 0 0   c 0 s e−iδ   c s 0  where 12 13 12 12 UPNMS =  0 c23 s23   0 1 0   −s12 c12 0  iδ 0 −s23 c23 −s23e 0 c13 0 1 deﬁning cos θ12 = c12 etc.

This is an active ﬁeld! Current status... 2 sin θ12 = 0.304 ± 0.014 2 sin θ23 = 0.51 ± 0.06 2 sin θ13 = 0.0219 ± 0.0012

Dr. Tina Potter 12. Beyond the Standard Model 17 Supersymmetry (SUSY) A signiﬁcant problem is to explain why the Higgs boson is so light.

f The effect of loop corrections on the Higgs mass should be to drag it up to the highest energy scale in the problem (i.e. HH unification, or Planck mass). f One attractive solution is to introduce a new space-time symmetry, “supersymmetry” which links fermions and bosons (the only way to extend the Poincarésymmetry of special relativity and respect quantum field theory.) Each fermion has a boson partner, and vice versa, with the same couplings. Boson and fermion loops contribute with opposite sign, giving a natural cancellation in their effect on the Higgs mass. f˜

+ HH f˜ Must be a broken symmetry, because we clearly don’t see bosons and fermions of the same mass. However, this doubles the particle content of the model, without any direct evidence (yet), and introduces lots of new unknown parameters. Dr. Tina Potter 12. Beyond the Standard Model 18 The Supersymmetric Standard Model

mixing SM : W ±, W 0, B −−−→ W ±, Z, γ ˜0 ˜0 ˜ 0 ˜0 mixing χ˜0 χ˜0 χ˜0 χ˜0 SUSY : Hu , Hd , W , B −−−→ 1, 2, 3, 4 ˜+ ˜− ˜ + ˜ − mixing χ˜± χ˜± Hu , Hd , W , W −−−→ 1 , 2 Dr. Tina Potter 12. Beyond the Standard Model 19 SUSY and Unification In the Standard Model, the interaction strengths are not quite unified at very high energy. Add SUSY, the running of the couplings is modified, because sparticle loops contribute as well as particle loops. Details depend on the version of SUSY, but in general unification much improved.

Dr. Tina Potter 12. Beyond the Standard Model 20 SUSY and cosmology

SUSY, or any uniﬁed theory, tends to have potential problems with explaining the non-observation of proton decay. For this reason, many versions of SUSY introduce a conserved quantity “R-parity”, which means that sparticles have to be produced in pairs. A consequence is that the lightest sparticle would have to be stable. In many scenarios 0 this would be a “neutralino” χ˜1 (a mixture of neutral “gauginos” and “Higgsinos”). 4.9% Cosmologists tell us that ∼ 25% of the mass in the Atoms universe is in the form of “dark matter”, which interacts ? ?? gravitationally, but otherwise only weakly. 26.8% Dark Matter 68.3% The lightest sparticle could be a candidate for the Dark Energy “WIMPs” (Weakly Interacting Massive Particles) which could comprise dark matter.

So there are several diﬀerent reasons why SUSY is attractive.

Dr. Tina Potter 12. Beyond the Standard Model 21 However, no sign of supersymmetry yet... On general grounds, some sparticles ought to be seen at energies around 1 TeV or lower. So LHC ought to be able to see them, especially squarks+gluinos ATLAS SUSY Searches* - 95% CL Lower Limits ATLAS Preliminary (high σ @LHC). December 2017 √s = 7, 8, 13 TeV miss 1 e,µ,τ,γ E dt[fb− ] √s = 7, 8 TeV √s = 13 TeV Model Jets T L Mass limit Reference R 0 χ˜0 st nd q˜q˜, q˜ qχ˜1 0 2-6 jets Yes 36.1 q˜ 1.57 TeV m( 1)<200GeV, m(1 gen. ˜q)=m(2 gen. ˜q) 1712.02332 → 0 χ˜0 q˜q˜, q˜ qχ˜1 (compressed) mono-jet 1-3 jets Yes 36.1 q˜ 710 GeV m(q˜)-m( 1)<5 GeV 1711.03301 → 0 χ˜0 g˜g˜, g˜ qq¯χ˜ 1 0 2-6 jets Yes 36.1 g˜ 2.02 TeV m( 1)<200 GeV 1712.02332 → 0 χ˜0 χ˜ χ˜0 g˜g˜, g˜ qqχ˜1± qqW±χ˜1 0 2-6 jets Yes 36.1 g˜ 2.01 TeV m( 1)<200GeV, m( ±)=0.5(m( 1)+m(g˜)) 1712.02332 → →0 ee,µµ χ˜0 g˜g˜, g˜ qq¯(ℓℓ)χ˜1 2 jets Yes 14.7 g˜ 1.7 TeV m( 1)<300 GeV, 1611.05791 → 0 - χ˜0 g˜g˜, g˜ qq(ℓℓ/νν)χ˜1 3 e,µ 4 jets 36.1 g˜ 1.87 TeV m( 1)=0 GeV 1706.03731 → 0 χ0 g˜g˜, g˜ qqWZχ˜ 0 7-11 jets Yes 36.1 g˜ 1.8 TeV m( ˜1) <400 GeV 1708.02794 → 1 GMSB (ℓ˜ NLSP) 1-2 τ + 0-1 ℓ 0-2 jets Yes 3.2 g˜ 2.0 TeV 1607.05979 GGM (bino NLSP) 2 γ - Yes 36.1 g˜ 2.15 TeV cτ(NLSP)<0.1mm ATLAS-CONF-2017-080 Inclusive Searches γ 0 GGM (higgsino-bino NLSP) 2 jets Yes 36.1 g˜ 2.05 TeV m(χ˜1)=1700 GeV, cτ(NLSP)<0.1 mm, µ>0 ATLAS-CONF-2017-080 / 4 Gravitino LSP 0 mono-jet Yes 20.3 F1 2 scale 865 GeV m(G˜)>1.8 10− eV, m(g˜)=m(q˜)=1.5TeV 1502.01518 × 0 χ˜0 g˜g˜, g˜ bb¯χ˜ 1 0 3 b Yes 36.1 g˜ 1.92 TeV m( 1)<600 GeV 1711.01901 gen. med. → χ0 ,µ χ˜0 rd ¯˜ 0-1 e 3 b Yes 36.1 g˜ m( )<200 GeV 1711.01901 ˜ gg, g tt 1.97 TeV 1 g ˜ ˜ ˜ 1 3 → 0 ˜ χ˜0 b˜1b˜1, b˜1 bχ˜1 0 2 b Yes 36.1 b1 950 GeV m( 1)<420 GeV 1708.09266 → χ0 χ χ0 b˜1b˜1, b˜1 tχ˜1± 2 e,µ (SS) 1 b Yes 36.1 b˜ 1 275-700 GeV m( ˜1)<200GeV, m( ˜1±)= m( ˜1)+100 GeV 1706.03731 → 0 0 t˜ t˜ , t˜ bχ˜± 0-2 e,µ 1-2 b Yes 4.7/13.3 t˜1 117-170 GeV 200-720 GeV m(χ˜1±) = 2m(χ˜ ), m(χ˜ )=55 GeV 1209.2102, ATLAS-CONF-2016-077 1 1 1→ 1 1 1 0 0 ,µ ˜ χ˜0 t˜1t˜1, t˜1 Wbχ˜1 or tχ˜1 0-2 e 0-2 jets/1-2 b Yes 20.3/36.1 t1 90-198 GeV 0.195-1.0 TeV m( 1)=1 GeV 1506.08616, 1709.04183, 1711.11520 → 0 ˜ χ˜0 t˜1t˜1, t˜1 cχ˜1 0 mono-jet Yes 36.1 t1 90-430 GeV m(t˜1)-m( 1)=5 GeV 1711.03301 → 0 gen. squarks t˜1t˜1(natural GMSB) 2 e,µ (Z) 1 b Yes 20.3 t˜1 150-600 GeV m(χ˜1)>150 GeV 1403.5222

rd ˜ ˜ ˜ ˜ ,µ ˜ χ˜0 3 t t , t t + Z 3 e (Z) t = 1706.03986 direct production 2 2 2 1 1 b Yes 36.1 2 290-790 GeV m( 1) 0 GeV → 0 t˜ t˜ , t˜ t˜ + h 1-2 e,µ 4 b Yes 36.1 t˜ 320-880 GeV m(χ˜ )=0 GeV 1706.03986 2 2 2→ 1 2 1 χ0 χ0 ℓ˜L,Rℓ˜L,R, ℓ˜ ℓ ˜1 2 e,µ 0 Yes 36.1 ℓ˜ 90-500 GeV m( ˜1)=0 ATLAS-CONF-2017-039 + + → 0 0 χ χ χ ˜ ,µ χ˜ ± χ˜ ˜ χ˜± χ˜ ˜1 ˜1−, ˜1 ℓν(ℓν˜) 2 e 0 Yes 36.1 1 750 GeV m( 1)=0, m(ℓ, ν˜)=0.5(m( 1 )+m( 1 )) ATLAS-CONF-2017-039 0 →+ 0 0 0 χ χ χ χ χ - χ˜ ± χ˜ χ˜± χ˜ ˜ 1± ˜1∓/ ˜2, ˜1 τν˜ (τν˜), ˜ 2 ττ˜ (νν˜) 2 τ Yes 36.1 1 760 GeV m( 1)=0, m(τ,˜ ν˜)=0.5(m( 1 )+m( 1)) 1708.07875 0 → → 0 0 0 0 χ χ ˜ ˜ ˜ 3 e,µ χ˜ ± χ˜ χ˜± χ˜ χ˜ ˜ χ˜± χ˜ ˜ 1± ˜2 ℓLνℓLℓ(˜νν),ℓν˜ℓLℓ(˜νν) 0 Yes 36.1 1 , 2 1.13 TeV m( 1 )=m( 2), m( 1)=0, m(ℓ, ν˜)=0.5(m( 1 )+m( 1)) ATLAS-CONF-2017-039 0→ 0 0 0 0 0 χ χ χ χ 2-3 e,µ 0-2 jets χ˜ ± χ˜ χ˜± χ˜ χ˜ ˜ ˜ 1± ˜2 W ˜1Z ˜1 Yes 36.1 1 , 2 580 GeV m( 1 )=m( 2), m( 1)=0, ℓ decoupled ATLAS-CONF-2017-039 EW 0→ 0 0 0 0 0 direct χ χ χ χ ¯ e,µ,γ χ˜ ± χ˜ χ˜± χ˜ χ˜ ˜ ˜ 1± ˜2 W ˜1h ˜ 1, h bb/WW/ττ/γγ 0-2 b Yes 20.3 1 , 2 270 GeV m( 1 )=m( 2), m( 1)=0, ℓ decoupled 1501.07110 χ0χ0 →χ0 ˜ → ,µ χ˜ 0 χ˜0 χ˜0 χ˜0 ˜ χ˜0 χ˜0 ˜2 ˜ 3, ˜ 2,3 ℓRℓ 4 e 0 Yes 20.3 2,3 635 GeV m( 2)=m( 3), m( 1)=0, m(ℓ, ν˜)=0.5(m( 2)+m( 1)) 1405.5086 → 0 - GGM (wino NLSP) weak prod., χ˜ 1 γG˜ 1 e,µ + γ Yes 20.3 W˜ 115-370 GeV cτ<1mm 1507.05493 0 → GGM (bino NLSP) weak prod., χ˜ γG˜ 2 γ - Yes 36.1 W˜ 1.06 TeV cτ<1mm ATLAS-CONF-2017-080 1→ + 0 χ˜ χ˜ χ˜ χ˜ ± χ˜± χ˜ χ˜± Direct 1 1− prod., long-lived 1± Disapp. trk 1 jet Yes 36.1 1 460 GeV m( 1 )-m( 1) 160 MeV, τ( 1 )=0.2 ns 1712.02118 + 0 ∼ χ˜ χ˜ χ˜ - χ˜ ± χ˜± χ˜ χ˜± Direct 1 1− prod., long-lived 1± dE/dx trk Yes 18.4 1 495 GeV m( 1 )-m( 1) 160 MeV, τ( 1 )<15 ns 1506.05332 0 ∼ Stable, stopped g˜ R-hadron 0 1-5 jets Yes 27.9 g˜ 850 GeV m(χ˜1)=100 GeV, 10 µs<τ(˜g)<1000 s 1310.6584 Stable g˜ R-hadron trk - - 3.2 g˜ 1.58 TeV 1606.05129 0 Metastable g˜ R-hadron dE/dx trk - - 3.2 g˜ 1.57 TeV m(χ˜1)=100 GeV, τ>10 ns 1604.04520 0 - χ˜0 Metastable g˜ R-hadron, g˜ qqχ˜1 displ. vtx Yes 32.8 g˜ 2.37 TeV τ(˜g)=0.17 ns, m( 1) = 100 GeV 1710.04901 particles → Long-lived 0 0 GMSB, stable τ˜, χ˜ τ˜(˜e, µ˜)+τ(e,µ) 1-2 µ - - 19.1 χ˜ 537 GeV 10

LFV pp ν˜τ + X, ν˜τ eµ/eτ/µτ eµ,eτ,µτ - - 3.2 ν˜τ 1.9 TeV λ311′ =0.11, λ132/133/233=0.07 1607.08079 → → Bilinear RPV CMSSM 2 e,µ (SS) 0-3 b Yes 20.3 q˜, g˜ 1.45 TeV m(q˜)=m(g˜), cτLS P<1 mm 1404.2500 + + 0 0 0 χ χ χ χ χ ,µ - χ˜ ± χ˜ ˜1 ˜1−, ˜1 W ˜1, ˜ 1 eeν, eµν, µµν 4 e Yes 13.3 1 1.14 TeV m( 1)>400GeV, λ12k,0 (k = 1, 2) ATLAS-CONF-2016-075 + +→ → 0 0 0 χ± χ χ χ˜ χ˜−, χ˜ Wχ˜ , χ˜ ττν , eτν 3 e,µ + τ - Yes 20.3 ˜ 450 GeV m( ˜1)>0.2 m( ˜1±), λ133,0 1405.5086 1 1 1 1 1 e τ 1 × →0 0 → - χ˜0 g˜g˜, g˜ qqχ˜1, χ˜ 1 qqq 0 4-5 large-R jets 36.1 g˜ 1.875 TeV m( 1)=1075 GeV SUSY-2016-22 RPV → 0 0 → χ0 g˜g˜, g˜ tt¯χ˜ , χ˜ qqq 1 e,µ 8-10 jets/0-4 b - 36.1 g˜ 2.1 TeV m( ˜1)= 1 TeV, λ112,0 1704.08493 → 1 1 → g˜g˜, g˜ t˜1t, t˜1 bs 1 e,µ 8-10 jets/0-4 b - 36.1 g˜ 1.65 TeV m(t˜1)= 1 TeV, λ323,0 1704.08493 → → t˜ t˜ , t˜ bs 0 2 jets + 2 b - 36.7 t˜ 100-470 GeV 480-610 GeV 1710.07171 1 1 1→ 1 t˜ t˜ , t˜ bℓ 2 e,µ 2 b - 36.1 t˜ 0.4-1.45 TeV BR(t˜1 be/µ)>20% 1710.05544 1 1 1→ 1 → 0 χ0 Scalar charm, c˜ cχ˜ 0 2 c Yes 20.3 c˜ 510 GeV m( ˜1)<200 GeV 1501.01325 Other → 1 *Only a selection of the available mass limits on new states or 1 phenomena is shown. Many of the limits are based on 10− 1 Mass scale [TeV] simpliﬁed models, c.f. refs. for the assumptions made. Dr. Tina Potter 12. Beyond the Standard Model 22 Signs of anything else?

CMS Preliminary 2.7 fb-1 (13 TeV, 3.8T) 104 ATLAS Preliminary EBEB Data Data 103 Fit model Background-only fit 102 ± 1 σ 2 Spin-2 Selection ± σ 2015: search for new boson Events / 20 GeV 10 2 s = 13 TeV, 3.2 fb-1 10 decaying to two photons, 10 Events / ( 20 GeV ) 1 X → γγ. 1 10−1

200 400 600 800 1000 1200 1400 1600 1800 2000 Bump at 750 GeV... 15

10 stat 2 5 σ In both experiments... 0 0 −5 -2

−10 (data-fit)/ Data - fitted background 200 400 600 800 1000 1200 1400 1600 1800 2000 400 600 800 1000 1200 1400 1600

mγγ [GeV] mγ γ (GeV) ATLAS 750 GeV local excess ∼ 3.5σ (global drops to 1.8σ) evidence, CMS 750 GeV local excess ∼ 2.9σ (global drops to 1σ) not discovery Revisited 8 TeV dataset and performed same analysis. Results are consistent... What could this be? Extra dimensions: excitations of gravitational ﬁeld in small, curled up, warped extra dimension – gives “towers” of spin-2 resonances, gravitons. Extended Higgs sector: add a second Higgs doublet to the SM – gives 5 (pseudo-)scalar Higgs bosons (lightest is the 126 GeV Higgs). Sadly, analysis of larger 2016 dataset showed no such resonance – a statistical ﬂuctuation Dr. Tina Potter 12. Beyond the Standard Model 23 Follow the results from LHC yourself!

http://atlas.ch http://cms.web.cern.ch http://lhcb-public.web.cern.ch/lhcb-public/

Dr. Tina Potter 12. Beyond the Standard Model 24 Summary

Over the past 40 years our understanding of the fundamental particles and forces of nature has changed beyond recognition. The Standard Model of particle physics is an enormous success. It has been tested to very high precision and can model all experimental observations so far. The Higgs “hole” is now becoming closed, though some other aspects of the SM are not quite yet under as much experimental “control” as one might wish for (the neutrino sector, the CKM matrix, etc). Good reasons to expect that the next few years will bring many more (un)expected surprises (more Higgs or gauge bosons, SUSY?).

Up next... Section 13: Nuclear Physics, Basic Nuclear Properties

Dr. Tina Potter 12. Beyond the Standard Model 25